Question about Dell Dimension 8400 PC Desktop

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I have a Dell 8400 that will not start up. The little green diode on the mother board lights, but nothing else happens. I read a post that suggested that I short the green and black wires of the motherboard power connector and plug in the power. Still nothing happens. I had the power supply tested with one of the handheld testing devices at Comp USA and they said it was good -- it did run and turned on all theiry green lights. But it still does not work for me. I also removed all cards and all memory and all cables disk cables. still nothing but the little green led. Can you help?

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  • 2 more comments 
  • bobteague200 Oct 05, 2010

    I still have no response. The power supply fan does not start. Absolutely nothing shows any response except the little green led beside the 24 pin connector, when the power is plugged in. absolutely nothing else. As I mentioned before, a Dell rep on the Dell users forum suggested, to others who had the same problem, that they put a shorting wire from the green wire to one of the black wires in the mother-board power connector (the 4 pin connector). That was supposed to make, force, the power supply run, but in my case it did not help. And yet, when Comp USA used the power supply tester, it showed that the power supply was good. Is it possible it is still bad in a way that the test tool did not check? Someone else, in a blog, suggested that the only real way to test a power supply is to replace it with a known good one.?? I don't have a known good one and I hate to buy one when Comp USA said this one is good. The problem started when I went on vacation. The system was working fine before. When leaving I shut down the computer and unplugged the UPS so that lightning could not run in on it. When I returned I plugged the UPS back and hit the start button on the 8400 -- but nothing happened, not a sound or anything. So, what else would you recommend?

    Thanks, Bob

  • bobteague200 Oct 05, 2010

    When I plug the jumper as you have shown, with the mother board connectors disconnected from the motherboard, then the fan turns. But if I plug the large motherboard connector into the motherboard, with the jumper in place from the back of the plug, then the fan does not start and only the green led turns on. So it appears that a signal from the motherboard is inhibiting the power supply.

  • bobteague200 Oct 06, 2010

    I have made a picture, but it is too large to send in this comment space. The maximum for here is 150KB. If you send me your email address, I will gladly send you one. My address is if you want to send your address that way.

    Otherwise, I am not sure what that accomplishes, since it is totally impossible to connect any of the connectors to the motherboard incorrectly. They are keyed and all of unique sizes. I do not have the jumper attached to the connector now, so that did not affect and does not now affect the operation.

    Thanks, Bob

  • bobteague200 Oct 06, 2010

    The solution has led me to a solution to the problem. Nonontech did a great job and my thanks to him for sticking with me.


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First remove the power cord from the back, disconnect everything, including mouse, keyboard etc..etc... now open the case and disconnect/unplug all the inner fan connector, cpu, ram, front panel connector, usb, audio, PCI, etc..etc..
Refer this:
I have a Dell 8400 - a02780f.jpg

[If there's Add-On graphic card, use the On-board one.]

Note all the connectors/plugs and their respective corresponding male/female connectors/slots. Once you are done disconnecting, remove the Bios Battery. Leave it outside for few minutes. Now install the battery, cpu, connect the cpu fan, install the ram (if there are multiple ram sticks, install only one of them), connect the hard drive, the front panel (only the power switch). Now connect both the power connectors (see above diagram, i've circled the power female connectors with red circles, there are two connectors..).


This is the labelled diagram of your motherboard.

Now power on the Machine and see what happens, if it's ok.. Switch off the machine, reinstall the remaining connectors and components one by one and power on the machine everytime you connect/install a component. Don't ignore this, otherwise you'll skip the most important part and you'll not be able to find out the culprit.

After several attempts and reboots, you'll see which one is causing the problem and you have to get rid of the particular component.

Let me know the result.

Good luck.

Thanks for using FixYa.

Posted on Oct 05, 2010

  • 4 more comments 
  • Lebanon Raingam
    Lebanon Raingam Oct 05, 2010

    Ok.. then, let's check the power supply (SMPS). Actually we can't judge good or bad, it depends on the usage, environment, or sometimes a luck :-) [I don't know how to say that..]. These days, Electronics are only warrantied, not guaranteed.. and that's the greatest problem for end users, but if Producers give guaranty, then they will loose many items..

    Well, look at the pic below:

    One end is connected to the Green and the other end to the black and in between them, there are two female connectors.. I hope you understand upto that. Take a tiny wire, but it, make the ends exposed and insert the ends as shown above. (Remove the four pin power connector from the motherboard). Now plug in the power cord and see if the SMPS' fan is running or not. If it doesn't, then the culprit is the smps.

    Let me know the result.

    Once again very good luck.

  • Lebanon Raingam
    Lebanon Raingam Oct 05, 2010

    No you shouldn't connect the Power connector with the wire in that way, it was only to check the SMPS. Well could you please upload a picture of the Motherboard with all the connections intact? If it's possible, will be much easier for me, if in case there's a small mistake with the connection. As you've mentioned, it shouldn't die :-) like that...

  • Lebanon Raingam
    Lebanon Raingam Oct 06, 2010

    Done on the other side.. :-)... Let me see.... only to clarify... Thanks.

  • Lebanon Raingam
    Lebanon Raingam Oct 06, 2010

    Now let's try this.. remove/disconnect/unplug everything from the motherboard, i.e. Ram, IDEs, SATAs, CMOS Battery, front panel, etc... Keep the CPU and CPU fan connected, both the power connectors connected. Also remove all the external peripherals, mouse, keybaord, monitor, etc..

    Connect the power cord, look carefully on the Front Panel connector, and short/jump the pin number 19 and 20

    Description of the Pins:

    1 INTRUDER 3 -> INTRUDER 3, FNT 32

    2 5v Power -> FNT 3, FNT 4

    3 5v Power -> FNT 2, FNT 4

    4 5v Power -> FNT 2, FNT 3

    5 LED VCC -> CTRL 6 thru R19,CTRL14 thru R20


    7 LED PSON


    9 GND -> GND

    10 GND? -> GND?

    11 GND -> GND

    12 USB 1 (bottom) Data - (white)

    13 USB 1 (bottom) Data + (green)

    14 GND -> GND

    15 USB 5V+ (both ports)

    16 GND -> GND

    17 USB 2 (top) Data - (white)

    18 USB 2 (top) Data + (green)

    19 GND -> GND

    20 PWR SWITCH LEFT SIDE (Both) --> CTRL 2

    21 Pin removed -

    22 HDD LED NEG -> CTRL 4


    24 ESUP LED NEG -> CTRL 13

    25 GND -> GND

    26 ?



    29 GND -> GND


    31 EXT_SPK 2 -> EXT_SPK 2


    33 EXT_SPK 4 -> EXT_SPK 4

    34 EXT_SPK 1 -> EXT_SPK 1

    Follow ups will next comment.....

  • Lebanon Raingam
    Lebanon Raingam Oct 06, 2010

    This is the final step and we'll definitely find out which component is the true "culprit". Remove the installed power supply, plug-in the connectors and power check with the new SMPS. It should at least show something, good or bad.

    Optional: If possible, check or try with another Processor, this is very rare but we need to try it this time.

    If either of these don't seem helpful, I would suspect the graphics card or the BIOS chip or in rare cases could be the ChipSet Module (IC). You'll need to take it to the service center or call Dell.

    I hope we've done all the troubleshooting methods.

    Let me also highlight the possible causes,

    1. Reset Button, when the reset button is stuck or not working or shorted, this happens (and we've known that this is not the case)

    2. Ram, when one or more Ram stick/s is defective, this could happen (neither this is the case)

    3. When CPU is overclocked, this will be cleared after the CMOS battery is removed and left for few minutes outside. (neither this)

    4. Power supply (checked and confirmed), but we can only test it's status, jumpering the green and the black wires.

    5. Front panel connector or front/ usb connector or etc..etc.. faulty... (no suspects.)

    6. Processor.

    etc.. etc..

    So the things we haven't tried out are, Video card, Bios (which is not possible from end users).

    Once again, Good luck...

  • Lebanon Raingam
    Lebanon Raingam Oct 06, 2010

    You are most welcome Bob... and once again thanks for using FixYa.


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